Breast cancer is the second leading cause of cancer death in American women. It is no surprise that women respond to a diagnosis of breast cancer with substantial psychosocial distress. Evidence from psychoneuroimmunology demonstrates that psychosocial distress impairs immune function by reducing natural killer cell activity (NKCA) and the production of interferon (IFN) gamma. Both NKCA and IFN gamma contribute to protection from tumor initiation, primary tumor growth, and tumor metastasis. Of note, epithelial tumors, like those of the breast, are responsive to NK cells and IFN gamma; hence, reductions in these forms of immune defense are relevant to breast cancer. We show that women diagnosed with breast cancer experience psychosocial distress, which is accompanied by elevated levels of cortisol, decreased NKCA, and reduced IFN gamma production. The purpose of this project is to determine whether epigenetic pattern underlies the mechanism for the immune dysregulation that occurs with a diagnosis of breast cancer. Aim 1 will longitudinally assess women diagnosed with early stage breast cancer and evaluate the trajectory of their psychosocial, cortisol, and immune response with respect to their peripheral blood mononuclear (PBMC) epigenetic pattern. In Aims 2 and 3, these relationships will be investigated at the cellular and molecular level. Aim 2 will determine whether PBMC epigenetic pattern is associated with changes in the cellular levels of IFN gamma and/or perforin, two key effector molecules in cancer control. Aim 3 will determine whether PBMC epigenetic pattern is associated with changes in chromatin accessibility for the promoter regions of IFN gamma and/or perforin. Lastly, Aim 4 will evaluate an explanatory model that posits mediated relationships among the psychobiological variables. Latent growth curve analysis will be used to identify and evaluate the trajectories of the study variables with regard to PBMC epigenetic pattern. This project will provide a mechanistic understanding of immune dysregulation, consequent to psychosocial distress, and has the potential to spur development of new approaches to identify and manage individuals at risk for psychosocial distress mediated immune dysregulation.